The present invention relates to a power converter using at least a semiconductor switching device.
In recent years, a power converter comprising a high-speed semiconductor switching device such as an insulated gate bipolar transistor (IGBT) has come to find wide applications. A large-capacity power converter, due to a large conduction current thereof, employs a large-capacity semiconductor switching device, sometimes in a set of several units in series or in parallel. In order to suppress the surge voltage at the time of switching, the inductance of the main circuit wiring is required to be reduced. For this purpose, the length of the conductor is decreased as far as possible or the width of the conductor is increased as far as possible using a tabular conductor. Further, an insulating material is often held between wide thin-plate conductors as a laminate conductor.
In a drive circuit for generating a control signal to control the on-off operation of the semiconductor switching device using an IGBT, for example, a predetermined voltage is applied between gate and emitter for the turn-on operation and a voltage is removed or a reverse voltage is applied for the turn-off operation. The gate-emitter voltage is controlled by performing the charge/discharge operation between gate and emitter through a gate resistor from a power supply included in the gate driver circuit. In the case where the gate wiring is located in the neighborhood of a main circuit conductor, the switching operation is affected by the magnetic field fluctuations due to the change in the main circuit current, with the result that a current imbalance between the switching elements connected in parallel or a malfunction is caused, sometimes leading to the breakage of the semiconductor switching device.
In the power converter disclosed in JP-A-9-261948, for example, the gate wirings of two IGBTs connected in parallel are arranged adjacently to the respective main circuit wiring to make a uniform effect that the current flowing in the main circuit conductor has on the gate wirings and thereby to suppress the imbalance between the IGBTs in parallel.
In the semiconductor stack described in JP-A-7-170723, on the other hand, a gate resistor is mounted on the bent portion of an end of each insulating plate making up a laminate conductor. In this way, the area of the loop formed by the gate wiring is reduced to alleviate the effect of the main circuit current.
In the former example, the use of a main circuit wiring made up of a tabular conductor to reduce the inductance of the main circuit wiring makes it difficult to form a structure in which the gate wirings are affected uniformly by each of the elements connected in parallel. As long as the IGBT module has a structure symmetric about a line, this requirement can be met by arranging the gate wiring at symmetric positions. Nevertheless, the IGBT module terminals are often asymmetric, and a structure symmetric about a line is difficult to construct. As a result, it is difficult for the gate wirings to be uniformly affected, resulting in an unbalanced current.
The latter example, on the other hand, requires the step of bending an insulating plate, which makes the fabrication difficult probably with an increased cost. Also, in the case where a main circuit wiring formed of a tabular conductor is used to reduce the inductance of the main circuit, the gate terminals of the IGBT may enter the wiring area of the main circuit. In such a case, the gate wiring are affected by the main circuit current.
The object of the present invention is to provide a power converter, comprising a main circuit wiring including a tabular conductor, that can reduce the effect of the main circuit current on the control signal wiring.
One means for solving the aforementioned problem is described below.
The control signal line for supplying a control signal to the control terminal of a semiconductor switching device includes the following portions defined based on the positional relation with the main circuit wiring and the main circuit current. They are that portion of the control signal line which is in opposite relation to an area of the main circuit wiring where a main circuit current flows and a plurality of tabular conductors are in superposed relation to each other, that portion of the control signal line which is in opposite relation to an area of the main circuit wiring where no main circuit current flows, and that portion of the control signal line located outside an end of the main circuit wiring. The sum of the lengths of the wiring of these portions is rendered substantially equal to the total wiring length of the control signal line.
The aforementioned means can suppress the effect of the main circuit current on substantially the whole control signal wiring. As a result, the malfunction of the semiconductor switching device can be prevented. Also, in the case where a plurality of semiconductor switching devices are electrically connected to each other, the imbalance of the control signals and the shift of the switch timing among the semiconductor switching devices can be prevented.
Another means for solving the problem is described below.
In the case where the control signal line passes in the vicinity of an end portion of the main circuit wiring, i.e. in the case where the control signal line crosses an end of the area of the main circuit wiring where the main circuit current flows, between the side of the main circuit wiring where a semiconductor switching device is located and the opposite side thereof, an arrangement is made so that the control signal line crosses an end of the area of the main circuit wiring where a plurality of tabular conductors are in superposed relation with each other.
As a result, even at a place in the vicinity of an end portion of a tabular conductor of the main circuit wiring which is otherwise easily affected by the main circuit current, the effect of the main circuit current on the control signal line is relaxed and the malfunction of the semiconductor switching device can be prevented.
Each means described above is applicable to various power converters including the inverter, converter, semiconductor valve and various switching power supplies.
Also, various semiconductor devices can be employed as a semiconductor switching device, such as the IGBT, MOSFET (metal oxide field effect transistor), GTO (gate turn off thyristor) and a switching module including any of these devices and other electric or electronic devices accommodated in a container.
According to this invention, there can be realized a highly reliable power converter using a main circuit wiring including a tabular conductor, which can operate in stable fashion while suppressing the effect of the main circuit current on the control signal.